View-transmission system



J1me 1942- v. K. ZWORIYKIN 2,285,551

VIEW TRANSMISSION SYSTEM Filed Dec. 20, 1958' 5 Sheets-Sheet 1 WITN ESSES: INVENTOR M I W ATTO EY June 9, 1942. v. K. ZWORYKIN 2,285,551

VIEW TRANSMISS ION' SYSTEM Filed Dec. 26, 1938 5 Sheets-Sheet 2 r INVENTOR V/ac/mwr (Zn 071077. BY & AT RNEY June 9, 1942. v. K. ZWORYKIN 2,285,551

VIEW TRANSMISSION SYSTEM Filed Dec. '20, 1958 5 Sheets-Sheet 5 WITNESSES:

INVENTOR ATDT NEY J 1 v. K. ZWORYKIN IEW TRANSMISSION SYSTEM Filed Dec 20, 1938 5 Sheets-Sheet 4 INVENTOR WITNESSES:

A'TT NEY' Patented June 9, 1942 UNITED STATE VIEW-TRANSMISSION SYSTEM Vladimir x. Zworykln, Forest nun, N. Y,-

slgnor to Westinghouse Electric & lllanulacturlng Company, East Pittsburgh, Pa., a corpov ration of Pennsyl Application December 20, 1938, Serial No. 24am 4 Claims. (01. m-m) My invention relates to view-transmission systems and it has particular relation to the lightsensitive devices used in such systems for the purpose of deriving a fluctuating electric current representative of a view or a picture being transmitted. This application is a continuationin-part of my application Serial Number 448,834, filed May 1, 1930, and of my Patent No. 2,141,059, both assigned to the Westinghouse Electric 8: Manufacturing Company of East Pittsburgh, Pa. Certain subject-matter herein disclosed is claimed in said application, in said patent, and in my applications Serial Nos. 220,206, filed July 20, 1938, and 346,260, filed'July 19, 1940.

In my copending application, Serial No. 376,117, filed July 5, 1929, and assigned to the Westinghouse Electric & Manufacturing Company, I have disclosed a view-transmission'system whereby a reproduction of a motion-picture film can be obtained electrically at a distance. The transmitting portion of the disclosed system comprises means for moving a film, longitudinally 7 thereof, at a constant speed adjacent'to a single photo-electric cell and means whereby the film, in its passage, is subjected to the action of a scanning-ray of light that moves rapidly from side to side across it.

In the operation of the system disclosed in my copending application, assuming that the film is advancing at the rate of 12 frames per second between the scanning ray and the photoelectric cell, that each picture frame" is scanned by one hundred transverse lines, and that each scanning-line is divided into one hundred linear picture-elements, it is apparent that each of the picture-elements is exposed to the light during a time interval of only $6 of a second and is represented by an infinitesimally small change in the output current from the photo-electric cell.

It would be highly desirable if the photoelectric cell could be exposed for a longer time to the light passing through each picture-element but, if the scanning rate is made lower, the picture could not be transmitted with sumcient rapidity to give rise to the illustion of m tion at the receiving end.

Since a reduction in the scanning rate is impracticable, attention has been paid to the development of photo-electric cells of greater sensitivity, and I have achieved a certain measure of success in that direction by the utilization of caesium oxide as a cathode material. The most sensitive cells known at present, however, must be followed by multi-stage amplifiers before thclr output currents, representing picture-elements, can be employed for controlling the transmission of energy to distant points.

Furthermore, the development of direct-view television systems 0! the type exemplified by the Another object of my invention is to provide an improved view-transmission system wherein a light-sensitive cathode-ray tube is employed.

A light-sensitive cathode-ray tube, constructed according to preferred embodiments of my invention, includes the following elements:

(A) A screen constituted by a plurality of minute light-sensitive elements that are insulated from each other and from ground;

7 (B) A common anode disposed .in spaced relation to the said elements;

(C) A common collector element mountedin spaced relation to said light-sensitive elements;

(D) A controllable means for producing a cathode ray; and

(E) Means for causing the ray to successively explore the rear surface of the screen.

When my improved cathode-ray tube is employed in a view-transmission system of either the direct or the indirect type, the view is focused continuously upon the entire light-sensitive face of the screen and the individual elementsthereof, by reason of their distributed capacity to ground, acquire positive charges proportional to the intensity and duration of the light.

The cathode-ray, as it explores the surface of v the source of the ray. The ray, however, each time it impinges upon one of the positively charged photo-cells, is robbed. of sufllcient elec- In order that the modulationof the electronic stream may be utilized, I interpose a resistor in the circuit to interconnect the collector-element and the cathode-ray source and connect the input terminals of an amplifier across the resistor. The output current from the amplifier may be used to control the radiation of modulated highfrequency energy or the transmission of energy I over metallic conductors to a plurality of viewreceiving stations.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, h'owever, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of certain specific embodiments when read in connection with the accompanying drawings, wherein Figure l is a diagrammatic view illustrating the usual way in which photo-electric cells are employed in television systems;

Fig. 2 is a simplified diagrammatic view of certain constituent .elements of an improved television system constructed according to one modification of my invention;

Fig. 3 is a diagrammatic view of a complete television system, constructed and organized according to a preferred embodiment of my invention, adapted to the purpose of transmitting filmfacsimiles or direct views;

Fig. 4 is' a plan view, partly in section, of an actual light-sensitive cathode-ray tube of the type shown diagrammatically in Fig. 3;

Fig. 5 is an end view, partly in section, of the light-sensitive electrode-assembly of the tube shown in Fig. 4;

Fig. 6 is an enlarged sectional view of the electrode-assembly taken along a line corresponding to the line VI-VI in Fig. 5;

Fig. 7 is a sectional view of the electrode-assembly taken along a line corresponding to the line VII-VII in Fig. 5; Figs. 8 and 9 are enlarged fragmentary front and rear views. respectively, of an electrodeassembly of alternative type;

Fig. 10 is a sectional view of the light-sensitiveelectrode-assembly illustrated in Figs. 8 and 9, taken along a line corresponding to the line X-X of Fig. 8; Y

Figs. 11 and 12 are enlarged fragmentary front and rear views, respectively, of a light-sensitlv screen of a further alternative type;

Figs. 13 and 14 are sectional views taken along the lines XIII-XIII and XIV-XIV, respectively, of the light-sensitive screen illustrated in Fig. 11;

Fig. 15 is a simplified diagrammatic view of a view-transmission system wherein a screen of the type shown in Figs. 11 to 14 is used;

Fig. 16 illustrates diagrammatically the concathode 5 that are interconnected through a potential-source 'l and a resistor 9, the resistor being disposed across the input terminals'of a suitable aperiodic amplifier II. A blocking condenser l3 preferably, is interposed between one terminal of the'resistor and the amplifier, and the negative terminal of the potential-source I may be provided with a connection [5 to ground,

, if desired.

When the photo-electric cell is exposed to the light that has passed through a moving film (not shown) from a transversely moving scanningray, or.to light that is reflected from an object from a similar scanning-ray, each picture-element is represented by an instantaneous minute change in the current flowing in the resistor 9, the amplitude of the current depending upon the intensity of the light and the duration of exposure of the cell to it. If, as previously mentioned', a single frame of a film passesbetween the scanning ray and the photo-electric cell in one second, and if the frame is scanned by one hundred lines, the photo-electric cell will be exposed to light representing one ten-thousandth of the frame-area during the very small timelnterval of 5 of a second.

Obviously the change in the output current from the photo-electric cell for such a short exposure is infinitesimal and, with the most sennections for one type of radio transmitter employing a modified form of tube differing from that illustrated in Fig. l; and,

Fig. 1'? diagrammatically illustrates the circuit connections for one type oi receiving tube suitable for use in connection with the transmitter system illustrated in Fig. 16.

In order that the principles underlying my invention may be thoroughly understood, a brief rsum of the action of the photo-electric cell shown in my copending application. Serial No. 376,117, hereinbefore referred to, will now be given in connection with Fig. 1 of the drawings.

The apparatus illustratedin Fig. 1 comprises a photo-electric cell i having an anode 3 and a sitive cells now available, it is the order of 3x 10- to 3X 10- amperes.

Since the limit in photo-electric cell sensitivity seems to have been substantially reached, an increase in cell output current must be obtained through a radical modification of heretofore known scanning methods. I propose, accordingly, to permit light from the view or picture being "televisioned" to fall continuously upon a screen constituted by a plurality of small photo-electric cells to store, in a plurality of individual reservoirs, the simultaneous output currents from the several cells and to thereafter successively discharge the current storage reservoirs at the scanning frequency in order to derive readily amplifiable currents representative of the picture-elements.

If the screen is to be used in television systems of the direct-view type, it may be of such size that the entire view can be focused th'r'eon; if it is to be used in film-facsimile systems, it may be constituted by a plurality of small photoelectric cells linearly disposed, since the travel of the film through the apparatus takes the place of the vertical component of the motion of the scanning ray. Inasmuch as the structure of the screen, insofar as the individual photo-electric elements thereof are concerned, is not dependent upon the dimensions thereof, it should be clearly understood that whenever the term screen is used hereinafter, either the linear or the planar type of screen is inferred. except in those instances where the meaning of the term is clearly determinable from the context.

The theory underlying the manner of operation of my improved view-transmission system will be clearly understood from a consideration focused upon the screen or from an illuminated translucent web, such as a motion-picture film. impinging 'continuously upon the photo-electric cell i I causes the upper plate of the condenser 25 to acquire a positive charge proportional to the intensity and duration of the light falling upon the cell. In order that the condenser may be discharged periodically, a similar photo-electric cell 21 and a resistor 28 may be connected in shunt relation thereto, and a light source (not shown) may be so disposed with respect to the second photo-electric cell as to illuminate it intermittently at the scanning rate.

Assuming that the cells i1 and 21 in Fig. 2 are representative of a single element of a screen of the linear type comprising any desired number of pairs of cells, one hundred for'exarnple. and that a magnified image of a motion picture film is caused to move across the screen. in a direction transverse to the linear extension thereof, it is evident that the eflfect of transverse scanning of the moving film by a vibrating light ray may be obtained by causing a ray of light to traverse, repeatedly, the cathodes of the cells i1 and 21 instead of the film. In such event, the discharge current from any individual cell,

representing the light from a single picture element, is as many times greater than if the film .were directly scanned by the light ray as the time of a single traverse of the discharge-ray across the entire screen is greater than the time required for the direct scanning of the said picture element. In other words, by causing the light to stay on the individual photo-electric element in my improved screen one hundred times longer, I am enabled to obtain one hundred tifnes more output current, representative of a. single picture element, than if a single large photoelectric cell were used.

By reason of manufacturing difdculties, however, it is quite expensive to provide each of the light-sensitive elements of the screen that are exposed to the view to be transmitted with an actual .storagecondenser and an individual condenser-discharging photo-electric cell. I have found it expedient, therefore, to utilize the distributedcapacity to ground of theindividual photo-electric cells as the storage reservoirs and to provide a source of cathode-rays for dissipating the charges stored in the said distributed capacity.

A further modification of my invention, therefore, as illustrated in Fig. 3 of the drawings, comprises an evacuated container 29- having a conical central portion 30, a circular front portion 3i and a cylindrical rear portion 32. A screen, constituted by a plurality of photo-sensitive cathodes 33 that are insulated from each other and from ground, is disposed within the front portion 3| of the container. Each cathode has a definite distributed capacity to ground which is indicated in the drawings by the condensers 34 shown in dotted lines. A common anode 35 is provided for all of the photo-sensitive cathodes, and potential is suppliedthereto from a common source 31.

Each individual cathode 33 has a conductive 1 portion 39 which extends rearwardly of the, screen, and a common collector-element 4i is disposed in spaced relation to all of the said portions and insulated therefrom. The collector element is connected to the negative terminal of the potential source 3'|,through a resistor 43. A conductor 45 extends from the negative terminal of the potential source 31 to ground. The ends of the resistor are connected, respectively, to the input terminals of an amplifier 46 that may be of any suitable type.

.A controllable source of cathode-rays. or an electron gun," is supported from a 'press" 41 disposed within the cylindrical rear portion 32 of the container 29. The "gun" comprises a thermionic cathode constituted by a metallic thimble 48 having an'active end portion 49, a cylindrical grid ii that surrounds the cathode and a cylindrical anode 53 disposed coaxially with the grid. The cathode is provided with a heater 54, preferably constituted by a filamentary resistor imbedded in vitreous material or clay (not shown). The thimble, grid and anode are preferably fabricated from non-magnetic material such as tantalum, or a 50% nickel-copper alloy.

Any suitable potential source 55 may be connected across the terminals of the heater, 54, and a single high potential source 51, the positive terminal of which is connected to ground, is provided for biasing the anode 53 and a focusing layer 59 of conductive material carried upon the major portion of the interior surface of the large end of the container positively with respect to the cathode.

In order that the cathode-ray shall be caused to repeatedly sweep over the backward-extending portions 39 of the photo-sensitive cathodes 33 and 63, is determined by the rate at which the charge builds up on the condenser, which rate is dependent upon the relative magnitudes of the condenser 65 and the resistor 69. v

Since it is necessary to cause'the ray to quickly return to its starting point at the end of each traverse, a short circuiting device is connected in shunt relation to the control condenser 65. The short circuiting device preferably takes the form of a thermionic triode 12 having an input electrode 13 normally biased negatively to the cut-off point by a source 15 of biasing potential and provided with means, such as a 480 cycle oscillator 11, for periodically overcoming the gridbiasing potential to thereby permit the shortcircuiting device to become conductive.

-It is highly desirable that the cathode-ray shall repeatedly traverse the screen in one direction only and that it shall be diverted therefrom during the return intervals. For that purpose, the primary winding J8 of a transformer 19 is connected between the anode of the short-circuiting tube and one terminal -of the condenser 65, and the secondary winding of the transformer together with a source iii of negative biasing potential is connected between the grid SI of the electron gun and the cathode thimble 48. The transformer-winding connections are so chosen that upon the fio'w of the condenserdischarge current in the short circuiting tube 12, sufflcient additional negative potential is applied to the grid iii of the electron gun, with respect to the cathode 48 thereof, to substantially cut oil? all electron-flow from the said cathode. The

cathode ray; therefore, is of normal intensity as it traverses the screen in one direction during the charging of the condenser 35, and is.of very low intensity as it returns to. the initial point preparatory to the next succeeding swing.

From the foregoing it will be seen that in the embodiment of my present invention, wherein a motion-picture film is televisioned'and moved at the proper rate with respect to the path traversed by the cathode ray, this path remaining substantially in a given plane perpendicular to the screen onto whichthe film is projected and the cathode ray deflected back and forth repeatedly across the image on the screen, that is,

. equivalent extent.

first in one direction along said-path from aninitial point and then back in the opposite or return direction to the'initial point, the result will be a scanning of the image along a sawtooth, the height or altitude of the teeth being determined by the amplitude or degree of defiection of the ray by the plates GI and 63, the pitch of the teeth or distance between adjacent tooth-points being determined by the rate of movementor travel of the film. When it is desired to employ the action just described, which I refer to as saw-tooth scanning, the adjustments in the system are such that the intensity of the cathode ray is normal as it traverses the screen in one direction but is of relatively low intensity as it returns in the opposite direction to that side of the screen from whence it started the preceding eflfective scanning movement.

When, however, the adjustmentsin the system are such that the electron flow from the cathode is entirely or substantially entirely cut oil upon and during discharge of the condenser 65, the result is that the cathode ray is put out at the beginning of and during the return movement backto that side of the screen from whence it will start the next effective scannin movement. The result of such action is that the screen is scanned by parallel lines, each starting at the same side of the screen and ending abruptly at the other side, these lines being made one after the other in rapid succession at a rate determined by the rate of charging and discharging of condenser 65. This method or manner of scanning I refer to as unilateral scanning.

In the operation of my improved system, when motion-picture films or the like are televisioned, an enlarged image of a minor longitudinal portion of. a moving film is cast upon the cathode screen by an appropriate optical system (not shown) in alignment with the lightsensitive elements thereof, as indicated by a plurality of arrows 83 in Fig. 3 which represent instantaneous light-intensities. Each individual cathode emits electrons under the insistor 63, consequently, is to an Each time, therefore, that the cathode-ray sweeps with full strength from one end of the screen to the other, the current through the resistor 43 is caused to pulsate. and thepulsations are amplified by the amplifier 43 for subsequent action of any suitable radio or wire transmitter.

It should be clearly understood in this connecmaterial modification for the direct televisioning" of illuminated animate or inanimate objects. When the system is organized for direct television, an image of the object is formed by appropriate optical means in the plane of the photo-sensitive cathodes constituting the screen, and the said image, through the use of a'rotating polygonal mirror. or a similar device, is caused to repeatedly move over the screen in a direction perpendicular to the linear extension thereof, thus simulating the movement of a film. For satisfactory results, the rate of movement of the image should be. such that at least twelve images per second are completely explored by the screen.

An actual cathode-ray device, except that the relative dimensions of the parts thereof may bewidely departed from in practice, of the type shown only diagrammatically in Fig. 3, is illustrated in Figs. 4, 5, 6 and 7, wherein the parts analogous to those of the tube shown in Fig. 3

are similarly designated.

As hereinbefore described, the device comprises an evacuated container 23 having a conical central portion 30, a circularfront portion 3| and a cylindrical rear portion 32 wherein the electron gunf is disposed.

The light-sensitive electrode-assembly is mounted in the circular end portion 3|. of the device and is constituted by a stack of interleaved metallic electrodes 35 and glass insulators 81 that are compressed between two lavite end plates 39 by a plurality of tie rods 9|.

Each end of each of the insulators 81 is shapedv to conform to the tie rod adjacent thereto in order that the insulators shall be prevented from.

' twisting, as indicated in Figs. 6 and '1.

fluence of the light impinging upon it and accharges, however, the cathode-ray is, successively, robbed of sufficient electrons for the neutralization thereof as it traverses the conductive extensions 39 of the photo-sensitive cath- Each of the metallic electrodes has a front bent-over silver-plated portion that carries one of the small photo-sensitive cathodes 33 and a rearwardly extending portion corresponding to the element 33 shown in Fig. 3. Each portion 39 has an opening 32 extending therethrough to accommodate the collector-element 4| that is' common to all of the portions 39 and is supported from the end plates 33.

The common anode 35 is also supported from the end plates 39 and is disposed closely adjacent to the cathodes 33.

The entire electrode assembly is supported by aplurality of rods 83 that are imbedded in a plurality of presses 93 and 9'! that extend inwardly from the periphery of the circular portion 3| of the tube. The-anode 35, the collector odes, and the electronic flow through the re- 73 ii and the tie rods 3| are, respectively, provided with leads 99,- IOI and I03 that-extend through the presses to the extent of the tube.

It will be noted from an inspection of Fig. 5, that the main tie rods 9| are electrically connected together and are indicated as being connected to ground. By reason of this fact, therefore, each of the photo-electrically. active cathodes 33 has a definite capacity to ground,

as indicated by the condensers 34 shown in;

dotted line in Fig. 3 of the drawings.

In the process of manufacturing my improved cathode-ray deviceafter the electron. gun and the unsensitized screen-electrode assembly are mounted within the container, the silver-plated surfaces .of the cathode-electrodes are oxidized .to a definite'degree by causing an electric di's-' charge to occur between two electrodes, such as silvered portions of the cathode-electrodes) that 1 contain a materiaLsuch as a mixture of caesium dichromate and silicon, which will free caesium when heated, is heated by high frequency currents induced therein by an internal coil. This frees the caesium and it is deposited upon the ends of .the electrodes carrying the oxidized silver coating.

The device is then heated to a temperature of between 150 and 200 centrigrade and maintained thereat until the silver-oxide-coated portions of the electrodes assume a rusty yellow color indicative of the completion of the sensitizing process. The color is probably caused by the formation of sub-oxides of caesium.

The device is next given a final exhaust to remove all residual gases and is sealed off from the pump.

It is also feasible to construct an electrode, assembly, of either the linear or planar type, by

the fusion together of a plurality of small cylinders of insulating material, the axes of which are parallel and perpendicular to the front and rear surfaces of the screen. Such screen is exemplified in Figs. 8, 9 and 10 of the drawings.

Referring specifically to Figs. 8, 9 and 10, a plurality of glass cylinders I05 are fused together to constitute an insulating support somewhat analogous in superficial appearance to an empty honeycomb. One face of'the composite insulator is provided with a metallic coating I01 by spraying from a Schoop-pistol or. by electroplating. A silver rivet Illa-extends through each of the small glass cylinders, the ends of each rivet being split and opened up slightly to prevent them from loosening. The split ends of the rivets are in capacitative relation to the conductive layer I01 which corresponds, in function, to the"collector element 4| shown in Figs. 3 and 4.

The rounded surfaces of the rivet heads are provided with layers of photo-electrically active material (not shown), such as caesium-oxide, and each rivet is thoroughly insulated from the neighboring rivets -by the glass cylinders.

When a screen of the type illustrated in Figs. 8, 9 and 10 is mounted in a cathode-ray tube of the typmhereinbefore described, a common anode element, analogous to the element 35 in Figs. 3 and 4, isdisposed in spaced relation to the photo-sensitive rivet heads. I

Instead of constructing the light-sensitive screen by assembling together a plurality of physically separate photo-cells, it also lies within the scope. of my invention to form the said cells in situ upon a single supporting member.

Referring-specifically toFig. 11, l2, l3 and 14 of the drawings, the supporting member, instead of being constituted by a plurality of glass cylinders, may be a metallic plate 3 having a plurality of openings 5 extending therethrough, or a .piece of woven metallic gauze.

In the preparation of the screen it is first entirely coated with a thin layer ll of material, such as porcelain and, thereafter it is thoroughly fired" to produce a glazed insulating coating.-

As an alternative method, the perforated sheet may be made of aluminum, the surface of which is oxidized, electrolytically or otherwise, to form the insulating coating.

The prepared sheet is next subjected to the.

action of a metal-spraying gun of the Schoop type and a great number of separated spots 9 of metallic silver are deposited thereon. The proper positioning ofthe silver spots may be assured by interposing a perforated plate between the gun and the prepared sheet or they may be deposited by any other convenient method such as sputtering, evaporation, or electrolytic deposition. Irre-. spective of the method employed, however, great precaution should be taken to ensure that the silver spots are each electrically disconnected from theothers since it is upon their complete insulation that satisfactory operation depends.

The plate carrying the silver spots is next subjected to an oxidizing process -to form a coating of silver oxide on each of the said spots. The

oxidation of the silver spots may be satisfactorily accomplished by subjecting the plate to'an electric discharge in an atmosphere of oxygen.

The final step in the process consists inheating the plate in the presence of vaporized caesium to render each of the silver spots photo-sensitive.

A sub-oxide of caesium is probably formed during the heating process but, of this fact, I am not quite certain.

The sensitive screen in its final form, therefore, comprises a conductive base, an insulating layer and a large number of small electrically separated photo-sensitive spots carried upon the insulating layer, portions of the peripheryv of each 'spot slightly overlapping the margins of the adja plate and extending the tube closely adjacent to the light-sensitivespots, and a single conductive to 1 the metallic plate that cathodes.

In order that the operation of the screen shall be understood when it is subjected to the simultaneous action of light and a cathode-ray, I have illustrated diagrammatically in Fig. 15 the elecconnection is made supports the said trical circuit of a single spot, to which figure attention should now be directed Referring specifically to Fig. 15, the condenser I23 represents the capacity of a single photoelectric spot I IS with respect to the supporting a resistor I21, a biasing ber of spots as N, then the total charging cur-,

rent for illumination of the entire screen under maximum light conditions is N'.[" amperes.

Now, if'the cathode-ray, in sweeping over the entire screen, in of a second, under the infiuence of a plurality of deflecting elements (not shown), has an intensity such that it will just completely neutralize the charge "6 of any one of the spots during an interval of time equal to M, then the discharge current will flow in the circuit in a direction opposite to that of the charging current, and its value for one element wilibeNtimesgrea-terthanthatof thecharging current thereto. Such being the case, the discharge current from a single element for an evenly illuminated screen will be equal to the total charging current for the entire screen. Inasmuch as the charging current may, for practical purposes, be regarded as devoid of fluctuations and, since the discharge current is constituted by a succession of impulses at very high frequency, it is comparatively simple to separate the discharge currents by properly designed filters and to amplify them before impressing them upon a transmitting medium.

It will, accordingly, be apparent that when a view, considered as comprising 11" view-elements, is impressed upon the sensitive screen. the charging currents to the tiny cells covered by the view, during 1 of a second are proportional to the varying light and shade of the viewelements. The discharge currents, representative of I successive view-elements when the cells are successively exposed to the scanning-ray are equal to the charging currents and, accordingly, are N" times greater than in television systems of the type wherein one or more photo-electric cells are momentarily exposed to light from suc-- cessive view-elements. For 100 line pictures, the photo-electric current is substantially 10,000 times as great as in conventional systems.

In the reception of a televisioned view, I prefer to utilize a tube such as is more fully described in Fig. 1'7, having a fluorescent screen over which -a cathode-ray is caused to move'in synchronism with the ray in the transmitting tube. The receiving tube is provided also with a control electrode interposed between the source of the ray and the screen, upon which electrode the received impulses, proportional to the instantaneous discharge currents of the minute photoelectric cells in the transmitting tube, are impressed to control the intensity of the ray. It is obvious, however, that other well-known receiving devices may. be utilized.

In Fig. 16, I show a modification of my invention in which the transmitting tube 29 of Fig. 3 is replaced by a tube in which the cathode ray is projected onto the face of a screen 32' which bears the photoelectric deposit. The screen may comprise aluminum sheet having a thickness of about half a mil and having on at least one side .an insulating coating which may, for example, be produced by oxidation of its surface in a m'annerwell known in the art. The screen 32' may be supported in a highlyevacuated vacuum-tight container 21' of glass or other suitable material having approximately the form illustrated in Fig. 16; -As an alternative modification, the screen 32' may consist of a thin sheet of mica or other suitable dielectric surfaced on one side with a conducting sheet. The screen 32' may be supported from the walls of the container 21' in any suitable-manner well known in the art and a conductor Iii may be sealed through the walls of the container 21' to make contact with the aluminum plate of the first-mentioned modification or to the conducting sheet surfacing one face of the-mica sheet in the other modification just mentioned.

At the opposite end of a prolongation of the container 21 is positioned an electron source such as an incandescent filament 29' between which and the screen is positioneda tubular anode-3i having an in-leading conductor I52 sealed through the glass walls of the container 21'. As'in the Fig. 3 modification, a metal electrode 30' having a small hole may be interposed between the electron source and the tubular anode, said hole being positioned approximately upon the extension of the axis of the.

as to impinge upon a point near the center of the screen 32'. At a suitable point between the tubular anode 3| and the screen 32' may be positioned a pair of deflecting plates 25', 26' similar to those in the Fig. 3 modification, these plates being adapted to deflect the concentrated electron beam was to cause the point of its incidence on the screen 32' to be varied. The electron stream is positioned so that its axis, when undefiected, makes an acute angle with the norman to the screen 32'.

The contour of the walls of the container 21' is made to have a comparatively large radius directly in front of the screen 32', and a suitable optical system 31' of a type well known in the art is provided for focusing an image of the view to be transmitted on the side of the screen 82' faced toward the anode ii. A coating I56 of silver or other suitable conductor may be formed on the inside surface of tube 21' in the region where the branch holding anode 2| enters the main chamber, and a lead I51 may be used to impress a potential more positive than anode- An output circuit adapted to modulate any suitable type of electrical transmission system, such as a wire telephony transmission line, a car-' rier current telephone transmission line, or a broadcast transmitter of any suitable type, may be adjustably connected by a pair of suitable taps to the resistor I55.

The surface of the screen 32' on which the optical image is focused has disposed upon it by means well known in the photoelectric cell art, a layer 26' of photoelectric material, such as potassium. If this potassium is deposited by condensation from the vapor phase, it will produce a layer in the form of separate particles or globules, and the distillation may be continued only until the potassium layer 38' is comparatively thin; that is to say, a layer of the thickness of 10- centimeters will usually be found adequate.

On the side of the photoelectric screen 82 on which the optical image is focused, and a short distance removed therefrom is positioned a collector electrode 36 in the form of a metallic screen of comparatively large mesh. It is usually possible to locate this screen in such a position that it is not in the focal plane of the optical system, and that accordingly no pronounced shadow of its parts is produced on the photoelectric surface 36. The collector electrode 39 is connected through a wire I53 sealed through the side of thecontainer 21 to an external circuit which may comprise a-source I54 of direct current electromotive force and a resistor I55, the opposite end of the resistor being connected to thelead Il previously mentioned.

The portions of Fig. 16 not already described illustrate one form of a suitable radio; broadcasting transmitting set.

The apparatus of the transmitting set I. comprises an antenna system 3' which is so tuned that it may oscillate at two separate and distinct frequencies. The oscillating circuit including the antenna 3 is connected on one side by means of a transformer 4 to the plate circuit of an amplifier triode 5'. The grid of the amplifier 5 is connected through a transformer 6' to the plate circuits of modulator triodes J and 8'. An oscillator triode 9', preferably of the radio frequency type is connected through a transformer ID to the grid circuit of the modulator triodes I and 8. The above arrangement comprises what is known as an ordinary pushand-pull transmitting arrangement.

By means of a transformer I I, the plate circuit of an amplifier I2 is also connected to the grid circuits of themodulator triodes I' and 8. The signal-output from tube 21' is impressed across the grid and plate of amplifier I2 by suitable variable taps to resistor I 55.

The oscillating circuit comprising the antenna 3' is also connected, by means of a transformer I3, to the plate circuit of an amplifier triode I4. The grid circuit of the amplifier I4 is connected, by means of a transformer I5, to the plate circuits of modulator triodes I6 and H. An oscillator triode I8, preferably generating a radio frequency different from that of oscillator 9, is conline relation to the time by current flowing into it fromthe source II through the resistor 69 across the photo-sensitive screen 32'. The rate mined by the rate at which the voltage of the v at which the cathode ray. is deflected 'from one side to the other side of the screen '32 is detercondenser I64 builds up, and this in turn is dependent in a way well known to those skilled in the art upon the magnitude of the source II, the resistor 69 and the intemal impedance of I the tube 61'. c When the cathode ray ly to the original starting-edge of the screen 32' by an arrangement in which a thermionic triode I2 is connected through a transformer windingnected, by means of a transformer I9, to the grid circuits of the modulator triodes I6 and II.

In the grid circuits of the triodes I6 and I I are connected respectively a pair of resistors I6I and I62 which are arranged by suitable, connections to impress upon the latter the terminal voltages of a pair of condensers I63 and I64 which are periodically charged and discharged at frequencies and wave forms suitable for deflecting a cathode ray to cause the latter to scan the screen of a television transmitter or receiver tube in the same way as is the condenser 65 in Fig. 3 hereof. Thus, the condenser I 64 is connected in shunt across the deflecting plates 25', 26 just as the condenser 65 of Fig. 3 is connected across the deflecting plates 6|, 63 therein. The condenser I64 is likewise shunted by a circuit consisting of a rectifier tube 61' (analogous to the tube 6! inFig. 3) and a resistor 69 (analogous to the resistor 69 in Fig. 3) connected in series with each other through a highpotential source II (analogous to the source II in Fig. 3). When thecondenser I64 has been discharged, its voltage gradually builds up in nearly a straightremains substantially linear.

I8 across the terminals of the condenser I64. Upon the control electrode I3 of the triodeI2'. is impressed a negative biasing voltage I5 in series with a source of periodic voltage pulses II which may, for example, be a l200-cycle oscillator (analogous to the oscillator 11 illustrated in Fig. 3). The periodicity of the pulses from the source 11' is made equal to the number of timesper second in which it is desired to have the cathode ray traverse the screen 32 from one edge to the other under the influence of the plates, 25', 26'. The source II, the resistor 69' and the internal impedance of tubes 61 and the electrical fleld between the plates 25 and 26 is able to deflect the cathode ray from one edge of the plate 32 to ;the other edge thereof. The

source TI is arranged so that the pulses which it impresses on the grid I3 of tube I2 are sufficient at their most positive value to just exceed the negative biasing effect of the source I5 and render the tube I2 conductive. The internal impedance of the tube I2 is so proportioned that when it is thus rendered conductive it can permit an extremely rapid discharge of the condenser I64- The duration of the positive pulse from the source 11 is made in a way readily apparent to those skilled in the art to exceed the bias source I5 only long enough for the condenser I64 to discharge thus to the desired degree, whereupon the tube I2 again becomes non-conductive and the condenser I64 starts to recharge through the source II, resistor 69 and tube 61'. As is well known to those skilled in the art, the voltage of the source II should be made so much higher than the voltage to which the condenser I64 has charged at the time the tube I2 becomes conductive that the charging rate of condenser I64 When the condenser I64 has its minimum charge, the voltage impressed on plates 25', 26 should cause the cathode ray to impinge on plate 32"at the point from which its traverse is desired to-begin.

A secondary winding in inductive relation with the winding I8 is arranged to impress on has been deflected to the desired extent, it is caused to return abruptflected in a direction normal to that already described by a pair of magnetic windings 26", 26" which are connected through a high resistance I66 in shunt with the terminals of condenser I66. The resistance I66 is preferably made so high relative to the inductanceof the coils 26" and 26" that the current through the latter has substantially the same wave form as the voltage across the terminals of condenser -I 66.

The condenser I66 is charged through a rectifler 61", a resistor 66" and a source H" in the same way as has been already described for condenser I66. Like the condenser I, the condenser I66 is arranged to be discharged through a shunt circuit comprislng a winding 16" and a triode 12" connected in shunt thereto The grid 13" of the triode 12" is controlled by a bias source 16" and a source 11" of positive voltage pulses. For example, the source 11" may be an oscillation generator having a frequency 7 of 12 cycles per second. In'generaL-the periodicity of the positive pulses of the source 11" is made equal to the periodicity with-which it is desired that the windings 26", 26" shall deflect I a the cathode ray from one side of thescreen 62' .larly described in connection with condenser I66,

the source 1|", the resistor 66" and the internal impedance of tube 61" are so proportioned that the condenser I66.v charges at a substantially linear time rate and acquires such a voltage during the period between successive positive pulses "between source 11" that the cathode ray in tube' 21' is deflected from one edge of the desired pic'- ture on the screen 22' to substantially the other edge.

Since the condensers I63 and I66 are in shunt to resistors I and I62 in the grid circuits of modulator tubes I6' and I1, the output of antenna 6' has impressed upon it modulations corresponding tothe wave form of the respective voltages of condensers 1162- and I66, and these modulations may be separated from the signals.

modulations emanating from oscillator 6' by suitable filtering arrangements well known to those skilled in the art and causedtosynchronize the deflections of the cathode ray at the receiving station with the movements of the cathode ray in the transmitter tube 21'. Likewise, the extinction of the cathode ray at the transmitting tube synchronously with the sudden discharge of condensers I63 and I66 modulates the Output from the antenna 3' to cause sudden variations in the amplitude thereof which are synchronous with the discharges of condensers I166 and I66, and these sudden amplitude variations will be impressed'upon the control electrode in the receiving system illustrated in Fig. 1'! and may be made to extinguish the cathode ray of the receiver tube synchronously'with the extinction of the cathode ray at the transmitting tube 21'.

In the receiving device in Fig. 1'1, an oscillating circuit 266, including an ,'antenna 26I, is adapted to be resonant to current of the frequencies generated by the oscillating circuits that include the triodes 6' and I6 oi the transmitting set. A detector tube 266 of well-known type is connected to the oscillating circuit 266. The output circuit of 'the amplifier triode 266 is connected to a grid 266m a cathode-ray tube 266.

The cathode-raytube 266 is constructed in a manner similar in many respects to the ordinary cathode-ray oscillograph and comprises a hot cathode 266, the grid 266, a tubular anode 251, plates 266 and 266 that are used to set up an electrostatic fleld and a fluorescent screen 266. The anode 261 of the cathode-ray tube 266 is supplied with high constant voltage from any suitable source 2" of direct current.-

The oscillating circuit 266 is also connected by means of a transformer 266 with a circuit 266. The circuit 266 is, in turn, connected by 'means of transformers 266 and 266 and suitable filters well known in the art with the grid circuit of the amplifying detectors 261 and 266 of suitable types well known .in the art. The output circuit of the detector 261 is connected by a suitable resistance coupling with the plates 266 and 266 of the cathode-ray tube 266, while the circuit of the detector 266 is similarly connected to the coils 269 and 216 that are associated with the cathode-ray tube 266 and so disposed with respect thereto that the magnetic fields generated by the coils are parallel to the electrostatic field generated by the plates 266 and 266.

The transformer 266 is so constructed that it acts as a wave trap for the particular wave that emanates from the tube 11' at the transmitting station of Fig. 16. In a like manner, the transformer 266 acts as a wave trap for the particular age at the terminals of resistor I6I in Fig. 16.

For this purpose, a resistor large relative to the reactance at the output frequency of tube 266 may be inserted in series with'windings 269, 216 if desired. By proper adjustments readily apparent to those skilled in the art, the cathode ray in tube 266 may be made to scan the screen 266 in synchronism with the cathode ray scanning of screen 62' in Fig. 16. It will be apparent, from a careful consideraon of the foregoing description of certain speciflc embodiments of my invention, that lightsensitive. cathode-ray tubes constructed in accordance therewith have a sensitivity,-by reason of the large output currents obtainable therefrom. which is many times greater than thesensitivity of a single photoelectric cell, no matter how large, when used in television systems constructed and organized according to the teachings of the prior art.

Furthermore, since scanning is accomplished by electronic means devoid of inertia, instead of by mechanical-means, my improved television transmitter is noiseless and does not easily get out of adjustment.

v In short, my invention provides means whereby the direct transmission of views of animate or inanimate objects can be accomplished and,

are substantially incapable of conducting electric current from the element to such bodies; in other words; there is no path capable of conducting substantial electric currents through the material connecting the element with adjacent 5 bodies.

' Although I have shown and described several specific embodiments of my invention, I am fully aware that many other modifications thereof are possible. My invention, therefore, is not to be 10 restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims. I

I claim as my invention:

1. View-producing apparatus whichcomprises 16 an image screen consisting of a plurality 01 insulation-supported conductive elements having electrically separated surfaces responsive to radiant energy, means for producing a concentrated electron-beam directed to impinge upon 20 at least one of said conductive elements, and means for deflecting said beamto cause it to successively scan said conductive elements.

2. View-producing apparatus which comprises an image screen consisting of a plurality of in-, 25 \sulation-supported conductive elements having electrically separated photo-sensitive surfaces, means for producing a concentrated electronbeam directed to impinge upon at least one of said conductive elements, and means for deflecting said beam to cause it to successively scan said conductive elements. I v

3. View-producing apparatus which comprises an image screen consisting of a plurality of insulation-supported conductive elements having electrically separated surfaces responsive to ra-i diant energy, means for producing a concentrated electron-beam directed to impinge upon at least one of said conductive elements, and means for deflecting saidbeam to cause it to successively scansaid conductive elements, an electron collector positioned near said conducting elements, and a path conductive for the electrons of said beam connecting said collector with the, first said means.

VLADIMIR K. ZWORYKIN. 

